rust-clippy/tests/ui/lifetimes.rs

// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![warn(clippy::needless_lifetimes, clippy::extra_unused_lifetimes)]
#![allow(dead_code, clippy::needless_pass_by_value, clippy::trivially_copy_pass_by_ref)]

fn distinct_lifetimes<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: u8) {}

fn distinct_and_static<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: &'static u8) {}

fn same_lifetime_on_input<'a>(_x: &'a u8, _y: &'a u8) {} // no error, same lifetime on two params

fn only_static_on_input(_x: &u8, _y: &u8, _z: &'static u8) {} // no error, static involved

fn mut_and_static_input(_x: &mut u8, _y: &'static str) {}

fn in_and_out<'a>(x: &'a u8, _y: u8) -> &'a u8 {
    x
}

fn multiple_in_and_out_1<'a>(x: &'a u8, _y: &'a u8) -> &'a u8 {
    x
} // no error, multiple input refs

fn multiple_in_and_out_2<'a, 'b>(x: &'a u8, _y: &'b u8) -> &'a u8 {
    x
} // no error, multiple input refs

fn in_static_and_out<'a>(x: &'a u8, _y: &'static u8) -> &'a u8 {
    x
} // no error, static involved

fn deep_reference_1<'a, 'b>(x: &'a u8, _y: &'b u8) -> Result<&'a u8, ()> {
    Ok(x)
} // no error

fn deep_reference_2<'a>(x: Result<&'a u8, &'a u8>) -> &'a u8 {
    x.unwrap()
} // no error, two input refs

fn deep_reference_3<'a>(x: &'a u8, _y: u8) -> Result<&'a u8, ()> {
    Ok(x)
}

// where clause, but without lifetimes
fn where_clause_without_lt<'a, T>(x: &'a u8, _y: u8) -> Result<&'a u8, ()>
where
    T: Copy,
{
    Ok(x)
}

type Ref<'r> = &'r u8;

fn lifetime_param_1<'a>(_x: Ref<'a>, _y: &'a u8) {} // no error, same lifetime on two params

fn lifetime_param_2<'a, 'b>(_x: Ref<'a>, _y: &'b u8) {}

fn lifetime_param_3<'a, 'b: 'a>(_x: Ref<'a>, _y: &'b u8) {} // no error, bounded lifetime

fn lifetime_param_4<'a, 'b>(_x: Ref<'a>, _y: &'b u8)
where
    'b: 'a,
{
} // no error, bounded lifetime

struct Lt<'a, I: 'static> {
    x: &'a I,
}

fn fn_bound<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
where
    F: Fn(Lt<'a, I>) -> Lt<'a, I>, // no error, fn bound references 'a
{
    unreachable!()
}

fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
where
    for<'x> F: Fn(Lt<'x, I>) -> Lt<'x, I>,
{
    unreachable!()
}

fn fn_bound_3<'a, F: FnOnce(&'a i32)>(x: &'a i32, f: F) {
    // no error, see below
    f(x);
}

fn fn_bound_3_cannot_elide() {
    let x = 42;
    let p = &x;
    let mut q = &x;
    fn_bound_3(p, |y| q = y); // this will fail if we elides lifetimes of `fn_bound_3`
}

// no error, multiple input refs
fn fn_bound_4<'a, F: FnOnce() -> &'a ()>(cond: bool, x: &'a (), f: F) -> &'a () {
    if cond {
        x
    } else {
        f()
    }
}

struct X {
    x: u8,
}

impl X {
    fn self_and_out<'s>(&'s self) -> &'s u8 {
        &self.x
    }

    fn self_and_in_out<'s, 't>(&'s self, _x: &'t u8) -> &'s u8 {
        &self.x
    } // no error, multiple input refs

    fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) {}

    fn self_and_same_in<'s>(&'s self, _x: &'s u8) {} // no error, same lifetimes on two params
}

struct Foo<'a>(&'a u8);

impl<'a> Foo<'a> {
    fn self_shared_lifetime(&self, _: &'a u8) {} // no error, lifetime 'a not defined in method
    fn self_bound_lifetime<'b: 'a>(&self, _: &'b u8) {} // no error, bounds exist
}

fn already_elided<'a>(_: &u8, _: &'a u8) -> &'a u8 {
    unimplemented!()
}

fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str {
    unimplemented!()
}

// no warning, two input lifetimes (named on the reference, anonymous on Foo)
fn struct_with_lt2<'a>(_foo: &'a Foo) -> &'a str {
    unimplemented!()
}

// no warning, two input lifetimes (anonymous on the reference, named on Foo)
fn struct_with_lt3<'a>(_foo: &Foo<'a>) -> &'a str {
    unimplemented!()
}

// no warning, two input lifetimes
fn struct_with_lt4<'a, 'b>(_foo: &'a Foo<'b>) -> &'a str {
    unimplemented!()
}

trait WithLifetime<'a> {}

type WithLifetimeAlias<'a> = WithLifetime<'a>;

// should not warn because it won't build without the lifetime
fn trait_obj_elided<'a>(_arg: &'a WithLifetime) -> &'a str {
    unimplemented!()
}

// this should warn because there is no lifetime on Drop, so this would be
// unambiguous if we elided the lifetime
fn trait_obj_elided2<'a>(_arg: &'a Drop) -> &'a str {
    unimplemented!()
}

type FooAlias<'a> = Foo<'a>;

fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str {
    unimplemented!()
}

// no warning, two input lifetimes (named on the reference, anonymous on Foo)
fn alias_with_lt2<'a>(_foo: &'a FooAlias) -> &'a str {
    unimplemented!()
}

// no warning, two input lifetimes (anonymous on the reference, named on Foo)
fn alias_with_lt3<'a>(_foo: &FooAlias<'a>) -> &'a str {
    unimplemented!()
}

// no warning, two input lifetimes
fn alias_with_lt4<'a, 'b>(_foo: &'a FooAlias<'b>) -> &'a str {
    unimplemented!()
}

fn named_input_elided_output<'a>(_arg: &'a str) -> &str {
    unimplemented!()
}

fn elided_input_named_output<'a>(_arg: &str) -> &'a str {
    unimplemented!()
}

fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) {
    unimplemented!()
}
fn trait_bound<'a, T: WithLifetime<'a>>(_: &'a u8, _: T) {
    unimplemented!()
}

// don't warn on these, see #292
fn trait_bound_bug<'a, T: WithLifetime<'a>>() {
    unimplemented!()
}

// #740
struct Test {
    vec: Vec<usize>,
}

impl Test {
    fn iter<'a>(&'a self) -> Box<Iterator<Item = usize> + 'a> {
        unimplemented!()
    }
}

trait LintContext<'a> {}

fn f<'a, T: LintContext<'a>>(_: &T) {}

fn test<'a>(x: &'a [u8]) -> u8 {
    let y: &'a u8 = &x[5];
    *y
}

// #3284 - Give a hint regarding lifetime in return type

struct Cow<'a> {
    x: &'a str,
}
fn out_return_type_lts<'a>(e: &'a str) -> Cow<'a> {
    unimplemented!()
}

fn main() {}